The present invention relates to fluids useful in subterranean applications and more particularly, to spotting fluid compositions that may be useful in subterranean applications for addressing, inter alia, drill string sticking problems.
Drill string sticking is a phenomenon in which a drill string or a portion of a drill string cannot be moved within a well bore. That is, a drill string or a portion of a drill string may experience sticking such that it cannot be rotated, reciprocated, or both. Drill string sticking is generally considered the most expensive and greatest lost-time problem in drilling.
Traditionally, the main types of drill string sticking are differential sticking and mechanical sticking. Differential sticking usually occurs when a drill string becomes embedded in, among other things, the filter cake contained within a subterranean formation, e.g., a permeable formation. A drill string can be become stuck in a well bore (e.g., in the filter cake) by a pressure differential between the hydrostatic pressure of the well bore mud and the formation pressure. This difference in pressures is sometimes referred to as “overbalance pressure.” The sticking force exerted on a drill string can be considerable when the overbalance pressure is exerted over a large portion of the drill string. Inadequate fluid-loss control, poor filter-cake characteristics, excessive solids content, and high overbalance pressures can exacerbate filter cake thickness and the severity of the problem. Mechanical sticking can be caused by, among other reasons, key seating, inadequate hole cleaning, well bore instability, and/or undergauge hole.
Methods used to alleviate a stuck portion of a drill string have included methods such as lowering the hydrostatic pressure in a well bore, applying a shock force just above the stuck point by mechanical jarring, placing a spotting fluid next to the stuck zone, or some combination of the above. Lowering the hydrostatic pressure of the well bore to free stuck pipe is one alternative, but this solution has drawbacks in that it may compromise well control. In many cases, application of a shock force to the pipe does not suffice to free the stuck pipe. Therefore, quick application of a spotting fluid is usually recommended as a solution for freeing stuck pipe. Indeed, the most common approach is to place a spot of oil, oil-base mud, or special spotting fluid in the stuck zone of drill string. Spotting fluids may act to assist in reducing the differential sticking problem encountered by drill strings by, among other things, acting as a lubricant and/or by dehydrating the filter cake formed around the stuck portion of the drill string.
A variety of spotting fluids have been heretofore used to address the problem of stuck pipe. One of the drawbacks of some of the spotting fluids heretofore used is that certain components of the spotting fluid may not be compatible with higher environmental standards of some regions. As one example of this problem, some spotting fluids use emulsifying agents that are not compatible with stricter environmental regulations of the North Sea region or other regions. Consequently, operators in some regions may have to resort to using less desirable spotting fluids that may be less effective or forego the use of spotting fluids entirely.